Method of cold working metals in the presence of a water-insoluble polysulfide



United States Patent Offi ce Patented Mar. 3, 1959 Fritz Singer, Starnberg, Upper Bavaria, Germany No Drawing. Application March 21, 1955 Serial No. 495,821

16 Claims. (Cl. 148--6.24)

This invention relates to a method of cold working (FeS and manganese disulfide (Mns metals. More particularly, the invention relates to cold working or plastic deformation of metal articles in l the presence of a su-lfidizing agent. The sulfidizing agentforms a sulfide coat or film with the metal on its surface, and the coat prevents the tool from biting into the article in the cold working operation.

This application is a continuation-in-part of my copending application, Serial No. 357,351, filed May 25, 1953, now abandoned, and the disclosure of the latter application is incorporated herein and made a part hereof by reference as fully as if it were set forth herein in its entirety.

In cold working metals, it is necessary to provide an intermediate layer between the metal to be worked and the tool or die, as otherwise, the tool would bite into the metal, resulting in damage to the tool and the metal surface to be worked. Numerous materials have been proposed for this purpose.

it has now been found in accordance with the invention that metals are very advantageously cold worked in the presence of a water-insoluble sulfidizing agent. The sulfidizing agent employed is a water-insoluble polysulfide having at least one loosely bonded sulfur atom, more particularly, a sulfur atom which is joined to another sulfur atom by a coordinate covalent bond. In the cold working operation, the polysulfide contacts or covers the metal surface within the zone or region of deformation.

Covering or coating with the polysulfide can be effected in several ways: by applying the polysulfide to the metal simultaneously or concurrently with deformation, adjacent the zone actually undergoing deformation, or on a part of the metal which is about to reach the deformation area of the die. Or the polysulfide can be applied to the metal shortly or considerably before it is to be worked, and then be allowed to remain on the metal until it is, deformed. The important ultimate requirement is that the polysulfide be present on the surface of the metal within the restricted or deforming part of the die, where the die operates on the work.

By chemical reaction between the sulfidizing agent within the zone of deformation, and the metal, when the metal is undergoing deformation, a coat'or film of metal sulfide forms on the surface of the metal and is strongly bonded thereto, and this coat prevents biting in of the tool. The' polysulfide is carried by the work into the die, and it reacts there at the same time as the work is being deformedfboth reaction and deformation taking place in the same zone. At the same time, a bonded metal sulfide coat forms on the die, by reaction with the metal of the die. Reaction takes place due to the heat produced as a result of the deforming operation. These coats not only function as protective layers on the metals, but they also function as lubricants to reduce friction. An accompanying advantage of cold working in the presence of the sulfidizing agent is that the agent itself functions as a lubricant, further reducing friction.

The water-insoluble polysulfides employed in the invention contain at least one loosely bonded sulfur atom and thus are capable of liberating elemental sulfur or readily decompose to liberate elemental sulfur. The loosely bound sulfur is released from chemical combination in the polysulfides at atmospheric temperature or on heating at a' moderately superatmospheric temperature, that is, at a temperature up to about 200 C. The sulfur in these compounds is very reactive and reacts with iron in the presence of water and even in the cold, i. e., at normal atmospheric temperature, to form iron sulfide. 7

These polysulfides include certain inorganic polysulfides, particularly, ferric sulfide (Fe S iron disulfide They also include organic polysulfides which contain sulfur joined by a coordinate covalent bond (also referred to as a semipolar or dative bond or linkage). These organic polysulfides contain a chain or group of at least three sulfur atoms, of which at least one is joined by a coordinate covalent bond. The polyethylenepolysulfides are representative, such as polyethylenepentasulfide and polyethylenetetrasulfide (-CH CH -S Other representative organic polysulfides are ethylxanthogentetrasulfide and factices, the latter being the reaction products of sulfur monochloride and rape oil or ricinoleic acid.

The polysulfides employed in the invention are to be distinguished from other polysulfides which contain only tightly bound sulfur and which will not furnish the results of the invention. For example, molybdenum disulfide (M08 will function as a lubricant, acting like graphite, and it may be welded to a metal surface at high pressure and temperature. However, molybdenum disulfide releases a part of its sulfur only at very high temperatures, so that the sulfur is not available for the formation of a metal sulfide with the metal undergoing deformation and the desired metal sulfide coat is not produced in cold working. Diphenyl disulfide is an example of an organic polysulfide which is unsuitable for use in the new method, because it contains only tightly bonded sulfur, with no sulfur joined to sulfur by a coordinate covalent bond. On the other hand, diphenyl trisulfide and diphenyl tetrasulfide contain sulfur joined by a coordinate bond and are useful in the invention.

The following are structural formulae of several representative polysulfides employed, illustrating the type of sulfur bonding which is required in the invention:

Iron disulfide:

Fe=S- S Ferric sulfide:

a s F l: S I Diphenyl tetrasulfide:

Ferric sulfide may be produced in colloidal form by adding sodium or ammonium sulfide to an aqueous solu- 3" I tion of ferric salts, washing the precipitated Fe,S; in anon-oxidizing atmosphere. The ferric sulfide is preferably used in the form of a paste to which hydroquinone is added to prevent oxidation.

Iron disulfide may be produced in colloidal form by adding ammonium polysulfide to aqueous solutions of ferric salts. Natural pyrite in wet or dry state with or .without additions of carbohydrates or other indifferent organic compounds and ground to colloidal particle size is a good sulfidizing agent.

For economic reasons, ferric sulfide and iron disulfide are particularly suitable, because they can be produced from spent cleannig acids available in metal plants, by oxidation of these spent acids and subsequent precipitation with sodium sulfide or sodium polysulfide. Metal plants were forced to dispose of these spent acids and had to use uneconomical processes to transform them into iron salts. The conversion to the iron sulfides and their use to facilitate metal working operations makes it possible for metal plants to use spent acids economically in their own operation.

Polyethylenepolysulfides are produced in colloidal form by treating ethylenedichloride with potassium polysulfide and may be used in drynnpurified form or in the form of a latex. Ethylxanthogentetrasulfide is produced by the action of sulfur monochloride on ethyl xanthogenate. I i The process is carried out by applying a composition containing the polysulfide to a metal article prior to or during the mechanical cold working or plastic deformation of the article, so that the cold working'is carried out with the sulfidizing agent covering the article. Since the polysulfides, especially the iron sulfides, are very susceptible to oxidation, it is preferable to coat the article with the polysulfide and deform the article immediately thereafter. This rapid succession of coating and deforming is also a modern production requirement.

The polysulfide may be used in dry form (but with a certain amount of water, as set forth subsequently), in

the form of aqueous pastes, or in aqueous suspensions. Which of these forms is used depends on the reactivity of the metal to be cold worked. The sulfidizing agent ventional lubricants applied to the surface of the wire. The sulfidizing agent can be used alone in dry powder form, as the sole agent providing the functions of coating and lubrication of the article, in the same manner as the dry lubricants in wire drawing are used, by pulling the article through a container arranged in proximity to the die and filled with the powder. Adhesives may be added, or the articles may be provided with a breath-thin layer of adhesives like glycerine and aqueous solutions of cellulose glycolate.

The reactivity of the polysulfides is enormously increased due to the heat and pressure prevailing in the die hole during the cold working operation, the surfaces of the metal article and the die becoming as hot as 200' C. and more, and there results an instantaneous formation of metal sulfide on the article being worked as well as on the die itself. The fact that a sulfide coating is likewise formed on the working surface of the die permits use of very cheap steels for making the dies instead of the very expensive tungsten carbide.

The reactivity of the polysulfides is further increased by the presence of water. However, the polysulfides and water are proportioned to' provide the die hole temperatures necessary for the reaction and formation of the proper sulfide coat. The water content is adapted to the conditions of cold working, that is, the reactivity of the metal, and the degree and speed of deformation. Thus, as any larger content of water would decrease the reactivity due to its cooling action, in cold working metals and alloys of high sulfur resistance, it is preferred not to use contents of water in the polysulfide larger than about ten percent.

is ordinarily provided on the metal in the cold, that is, at

nonnal atmospheric temperature. The agent is applied, for example, by passing the article through a container of the dry agent or in the form of a paste, by immersing the article in a bath, by spraying, or by drying a dispersion on the article prior to working. The method of application and the contents of the composition applied vary with the work, the ingredients of the composition and the type of operation. 1

As an exemplary method of application, in tube drawing, the tube can be passed through a container filled with a polysulfide paste and next through the die. An article to be extruded can be dipped into a paste and then extruded. A liquid composition can be poured over the die and the work during the deformation, but this method is not preferred because of the likelihood of oxidation of the polysulfides and it is not economical.

The mainfields of application of the present process are cold drawing and cold extrusion of metals, especially in wire, profile and tube drawing, in which concentrates polysulfides of the invention may be used in the same manner by spraying the wire with or dipping it into a suspension or colloidal solution of the sulfidizing agent, allowing it to dry, and then drawing it with the aid of con- At the same time, some water must be present, for rapid reaction 'to produce a sufficient sulfide coat very quickly. The quantity need not be great but may be that remaining when an aqueous paste or suspension of the polysulfide is allowed to dry in the atmosphere, that is, on the order of one to three percent.

As the reactivity of the polysulfide is to a high degree dependent upon the temperature, starting the operation with cold tools would result in an inadequate formation of the sulfide film until the working temperature of the die was reached. A preferred method involves heating the die at the start or after interruptions of operation to about 50-400 C.

In the practice of the invention, sulfidizing compositions having a relatively low content of the polysulfide provide successful working of metals such as low carbon steels or pure iron which are highly reactive in forming metal sulfides. In working such metals, it is preferable to employ compositions having a minimum polysulfide content of about 20%, for rapid reaction and production of a sulfide coat which will fill the requirements. However, for cold working metals of high sulfur resistance such as steels of higher carbon and/or alloy content, higher percentages of polysulfide are preferred; that is, compositions having greater than about 40% by weight of the polysulfide are preferred for such resistant steels and alloys, for successful working. It is further preferred to use a composition containing greater than about 60% of polysulfide for the most resistant metals. The foregoing polysulfide contents have reference to compositions in which the polysulfide is the sole sulfidizing agent. A polysulfide may also be used in conjunction .with another sulfidizing agent, such as colloidal sulfur, as disclosed in my copending application Serial No. 460,503, filed October 5, 1954. The polysulfide content may then be reduced accordingly, and with colloidal sulfur, the total content of sulfidizing agents may be reduced below the foregoing values, due to the greater reactivity of colloidal sulfur.

When the inorganic or organic polysulfide is produced by wet methods and contains more water than is desired and particularly, when it is desired to provide a composition having a very high polysulfide content on the metal, such compositions may advantageously be used by dipping the work pieces into the aqueous suspension or paste of the polysulfide to provide a film of the suspension on the articles, allowing the suspension adhering to the work piece to dry in the open air, and cold working the work pieces thus provided with a film of residual moisture-containing polysulfide with or without the application of conventional lubricants or other assistants. Resiccation of the suspensions prior to application would require precautionary measures to avoid oxidation or loss of their colloidal properties. It is preferred for high reactivity to employ the polysulfides in colloidal form, which is meant to include semi-colloidal or approaching colloidal particle size.

When an article is coated with the polysulfide before the cold working, the sulfur is sufficiently reactive to produce a sulfide film on the article. Also, the sulfidizing agent is a lubricant. However, the article is not protected thereby sufliciently for the working, and the proper formation of a sulfide coating which will serve the intended purpose takes place in the region of the die at the elevated temperatures prevailing there, where the metal surface contacts the die. Consequently, the article is covered with an excess of the polysulfide over the relatively small amount which reacts prior to reaching the die hole, so that there is unreacted polysulfide present completely over the surface as it reaches the hot area at the zone of deformation, within which the effective coat forms.

In order to reduce friction of the work in the die and the hardening effect-of cold working, additions of conventional lubricants of any type used in cold working metals may be made. Preferred conventional metal working lubricants are long chain fatty alcohol sulfonates and water-insoluble soaps, for example, calcium or aluminum stearates, and oil-in-water emulsions.

Other lubricants suitable for use with the sulfidizing agent are'described in the above application Serial No. 357,351. A conventional lubricant may be included in one lubricating composition with the polysulfide, or the two may be applied separately. Thus, the article may be provided with a coating of polysulfide, and then the cold working may proceed in the further presence of the lubricants.

The amount of conventional lubricant may be reduced considerably below that previously used, since the inorganic and organic polysulfides employed in the invention have suflicient lubricating properties in colloidal or semi-colloidal form. To obtain the maximum sulfidizing effect with adequate lubrication, the conventional lubricant may be reduced to several percent and may even be omitted entirely.

The amounts of the ingredients of the sulfidizing agent compositions according to the invention depend on the reactivity of the metal to be worked to form metal sulfide. Low carbon steel, for instance Armco iron, the reactivity of which in contact with sulfidizing agents is extremely high, can be successfully worked with a mixture of:

35% of ferric sulfide, iron disulfide, or polyethylenetetrasulfide paste containing about 60% sulfide, the balance being water, and

65% of a cutting oil emulsion containing about 50% of cutting oil and 50% of water, the cutting oil being composed, for example, of about 86% of a mineral oil and about 14% of an emulsifier.

The above and the other proportions given in the specification are by weight.

For cold working steels of up to 0.25% carbon content, the following mixture can be employed:

70% of ferric sulfide, manganese disulfide or diphenyl trisulfide paste containing about 60% sulfide-and the balance of water, and

30% of the above cutting oil emulsion.

In cold working less reactive metals, for instance steels of higher carbon and/or alloy content, higher per centages of sulfidizing agent in the mixtures are preferred, for example, as in a mixture which is composed 60% of ferric sulfide paste containing about 60% ofcolloidal Fe S the balance being water, 30% of colloidal sulfur containing about 50 to 60% of sulfur, the balance being water, and

10% of ammonium dodecylsulfonate.

Preferred high-sulfur compositions, for very resistant metals, are, for example:

% of ferric sulfide or iron disulfide containing 10% water, and 10% of calcium stearate.

and

90-95% of the unpurified reaction product of potassium polysulfide and ethylene dichloride, having a water content of 10%, and

10-5% of aluminum-stearate.

A polysulfide may be used'alone,without the addition of conventional lubricants, either in aqueoussuspension, in aqueous pastes or as a powder, depending on the reactivity of the metal, the reduction rate and the moldability of the metal. 4

In applying the polysulfide in the aforesaid manner, additions of wetting agents such as fatty alcohol sulfonates (which can also be employed as lubricants, as described above), and adhesive agents such as methyl cellulose and cellulose glycolate, to the aqueous suspensions of the polysulfides may advantageously be used in order to insure a uniform wetting of the metal surface, a uniform distribution of the polysulfide on and the necessary adhesion thereof to the metal surface. The work pieces are dipped in the suspension, and the adhering film of the suspension is allowed to dry in the air. Since the inorganic sulfides oxidize readily and lose a portion of their sulfur even at low temperature, an antioxidant, such as hydroquinone, is included in the suspension to prevent oxidation during drying.

In such an application of ferric sulfide, 2 parts by weight of cellulose methyl ether or cellulose glycolate and 1 part of hydroquinone may be dissolved in parts by weight of an aqueous paste of ferric sulfide containing about 60% of the sulfide and the balance of water. To this mixture, 2 parts by weight of dodecylbenzolsulfonate are added and dissolved. The articles to be cold worked are dipped into this mixture and then allowed to drain and dry in the open air. In this connection, it is to be noted that no such drying operation is carried out as will decompose the sulfide or cause loss of its colloidal properties. As soon as the articles are visibly dry, but still containing residual water, they are cold worked, by

drawing or extrusion. The proper sulfide film forms in the short period of time during which the work piece passes through the deforming tool, reaction taking place at the zone of deformation, where the piece becomes hot due to the deformation and friction with conduction of the heat.

The sulfidizing agents employed in the invention are very cheap, and the process is simple and economical. Consequently, when the metal undergoes a series of progressive reductions or deformations, it is recommended that the sulfidizing agent be applied to the work in each cold working operation.

The sulfide coat or film produced according to the invention, although thin. has proved to be very elfective in facilitating the cold plastic deformation of metals and fide is preferably the sole agent producing a coat bonded to the surface of the article. The invention obviates the sufiicient to form a bonded protective coat of metal sulseparate production of a bonded sulfide coat by 'combining the coating and cold working in one operation in one zone, the deformation zone. Where the polysulfide is continuously provided in contact with the metal article, there is the advantage that if the coating is damaged by the tool, it is immediately and continuously renewed. The reaction forming sulfide with the metal is very rapid, as itmust be'in order to be effective. Thus, the invention has important advantages over prior methods and provides a very simple and economical process.

The water-insoluble polysulfides employed in the invention provide certain advantages over the water-soluble sulfidizing agents. They are odorless and not poisonous. Water-soluble agents such as ammonium sulfide require the. presence of oxygen for formation of the metal sulfide, according to the'equations.

The invention is hereby claimed as follows:

1. In a method of cold working a metal article, the step which comprises plastically deforming the article in contact with a water-insoluble polysulfide containing at least one sulfur atom which is joined to another sulfur atom by a coordinate covalent bond and water, said polysulphide being present in an amount sufficient to form a bonded protective coat of metal sulphide on the surface of the article within the zone of deformation.

2. A method according to claim 1 in which the water content of the polysulfide is a' maximum of about 10% by weight.

3. In a method of cold working a metal article, the step which comprises plastically deforming the article after coatingthe article with a water-insoluble polysulfide and water, said polysulfide being present in an amount of at least by weight and containing at least-one sulfur atom which is joined to another sulfur atom by a coordinate covalent bond.

4. A method according to claim 1 in which the polybond and water, said polysulphide present in an amount phide on the surface of the article within the zone of deformation and said composition also containing a water insoluble soap lubricant. Y 8. In a method of-cold working a metal article, th step which comprises plastically deforming the article in contact with an aqueous composition containing a waterinsoluble polysulfide containing at least one sulfur atom which is joined to another sulfur atom by a coordinate covalent bond and water, said polysulphide being present in an amount sufficient to form a bonded protective coat of metal sulphide on the surface of the article within the.zone of deformation, the polysulfide. and water in protective coat of metal sulfide is formed on the surface of the article within the zone of deformation.

10. In a method of cold working a metal article, the,

step which comprises plastically deforming the article in contact with iron disulfide and water, said polysulphide being present in an amount sufficient to form a bonded protective coat of metal sulphide on the surface of the article within the zone of deformation.

11. In a method of cold working a metal article, the step which comprises plastically deforming the article in contact with manganese disulfide and water, whereby a bonded protective coat of metal sulfide is formed on the surface of the article within the zone of deformation.

12. In a method of cold working a metal article, the step which comprises plastically deforming the article in contact with a sufficient amount of an organic polysulfide containing at least one sulfur atom which is joined to another sulfur atom by a coordinate covalent bond and water, whereby a bonded protective coat of metal sulfide is the sole agent providing coating and lubrication of the article.

5. A method according to claim 1 in which the tools are heated at the start of operation.

6. In a method of cold working a metal article, the steps which comprise providing the article with a film of an aqueous suspension of a water-insoluble polysulfide containing at least one sulfur atom which is joined to another sulfur atom by a coordinate covalent bond, allowingthe film to dry in the atmosphere to a moisture content of about 1-3%, and plastically deforming the thus coated article, the amount of said polysulfide present in said dry film-being sufficient to form a bonded protective coat of metal sulfide on the surface of the article within the zone of deformation.

7. In a method of cold working a metal article, the step which comprises plastically deforming the article in contact with a composition containing a water-insoluble polysulfide containing at least one sulfur atom which is joined to another sulfur atom by a coordinate covalent sulfide is formed on the surface of the article within the zone of deformation.

13. In a method of cold working a metal article, the step which comprises plastically deforming the article in contact with a sufficient amount of a polyethylenepolysulfide containing at least one sulfur atom which is joined to another sulfur atom by a coordinate covalent bond and water, whereby a bonded protective coat of metal sulfide is formed on the surface of the article within the zone of deformation. 1

14. A method according to claim 6 further defined in that said polysulphide is present in a composition containing substantially 20% by weight of polysulphide.

15. A method according to claim 1 in which conventional lubricants form an additional ingredient to reduce friction.

16. A method according to claim 1 in which colloidal sulphur forms an additional ingredient.

References Cited in the file of this patent UNITED STATES PATENTS I France Mar. 19, 19.45 

1. IN A METHOD OF COLD WORKING A METAL ARTICLE, THE STEP WHICH COMPRISES PLASTICALLY DEFORMING THE ARTICLE IN CONTACT WITH A WATER-INSOLUBLE POLYSULFIDE CONTAINING AT LEAST ONE SULFUR ATOM WHICH IS JOINED TO ANOTHER SULFUR ATOM BY A COORDINATE COVALENT BOND AND WATER, SAID POLYSULPHIDE BEING PRESENT IN AN AMOUNT SUFFICIENT TO FORM A BONDED PROTECTIVE COAT OF METAL SULPHIDE ON THE SURFACE OF THE ARTICLE WITHIN THE ZONE OF DEFORMATION. 